1. Field of the Invention
The present invention relates to a polarizing plate grading method and especially relates to a method of grading the polarization plate based on the value obtained by dividing the difference of the net chromatic difference values measured on two polarization plates by the net chromatic difference value of one of the polarization plates.
2. The Prior Arts
Usually, the liquid crystal display has the benefits of high image quality, small volume, light weight, low driving voltage, low power consumption, and wide application range. As such, it has been widely utilized in the following devices: small, to medium-sized portable TVs, mobile phones, camcorder-players, notebook computers, desk top displays, projector TVs, consumer electronics or computer products. Thus, the liquid crystal display gradually replaces the Cathode Ray Tube (CRT) as the mainstream of display. The polarizing plate 10 or the polarizing film is one of its key components. The functions of the polarizing plate 10 are to filter out lights in unspecific directions, so as to become the light in the specific direction (polarized light). The two upper and lower polarizing plates 10 are arranged on a LCD substrate, and the directions of polarization lines of the upper and lower polarization sheets 10 are mutually perpendicular to each other. The light passing through the lower polarizing plate 10 can not pass through the upper polarizing plate (and it will appear as a dark color) as shown in FIG. 1A. However, if the direction of the molecules of liquid crystal layer 20 disposed therebetween is rotated by the manipulation and control voltage, then the direction of the polarizing light transmitted through the lower polarizing plate 10 can be directed and rotated 90° and pass through the upper polarizing plate 10 (and it will appear as a bright white color). As such, the panel will indicate the variation of brightness and darkness of light as shown in FIG. 1B. Briefly speaking, the major function of the polarizing plate 10 is to convert ordinary natural light without polarization (non polarized light) into polarized light, so as to make the light enter the liquid crystal layer 20 as polarized light.
However, due to the intrinsic property of the material of the polarizing plates 10, the problem of mura will inevitably appear during assembly of the polarizing plate 10, wherein the problem of edge mura will most frequently occur. As shown in FIG. 2, the polarizing plate 10 can roughly be divided into four-color blocks M1′, M2′, M3′ and M4′ based on its difference of brightness and darkness and un-uniform distribution of colors. Since the problem of mura on the present polarizing plate market still lacks a publicly recognized examination standard, the examination standard of each manufacturer is different. Thus, manufacturers usually do not accept the examination results of other manufacturers, and this sometimes leads to problems between the seller and the buyer of the polarizing plates 10.
Therefore, there exists the need in the market for standardizing polarizing plate grading methods, so as to solve the above-mentioned problem.